1. Field of the Invention
The present invention generally relates to stiffener structures used on flexible substrates on which electrical components are mounted and, more particularly, to improving the adhesion of stiffener structures to flexible substrates.
2. Background Description
FIG. 1a shows an electronic module 8 that includes a stiffener structure 10 affixed by an adhesive 12 to a flexible substrate 14. The stiffener 10 maintains a region 16 of the flexible substrate 14 in a substantially planar orientation such that an electronic component 18, such as an integrated circuit chip or multilayer circuit package, can be connected to electrical wiring (not shown) on the surface of the substrate 14. These stiffener structures 10 may be used in connection with taped ball grid array devices or other electronic modules or packages. The substrate 14 is generally highly flexible and very thin (i.e., less than one tenth of an inch). Polyimides, such as KAPTON.RTM. available from DuPont, as well as other organic materials have been used as flexible substrates 14 for electronic components 18. The stiffener 10 typically will have an opening that allows the electrical component 18 to be affixed to the substrate 10 within the stiffener 10 opening after the stiffener is secured to the substrate.
FIG. 1b shows the underside of the electronic module 8. The electronic component 18 and region 16 are shown as dashed lines through the flexible substrate 14. Electrical connections (not shown) from the electrical component 18, are electrically connected to wiring 20 or ball connectors 21 on the flexible substrate 14, and the wiring 20 and/or ball connectors 21 are then used to secure the module 8 to a card or other suitable substrate (not shown). Vias (not shown) or other electrical connection configurations can be used to connect the electrical component 20 to the wiring 20 or ball connectors 21.
FIG. 2 shows an example electronic component 18 having a plurality of ball connectors 22. Contrasting FIG. 1b with FIG. 2, it can be seen that the ball connectors 22 are used to electrically connect the electrical component 18 to the wiring 20 and ball connectors on the flexible substrate 14. The ball connectors 22 are connected to electrical structures (i.e., transistors, resistors, capacitors, etc.) within the electrical component 18 are used to electrically connect these structures to circuitry positioned outside the component 18. If region 16 of substrate 14 is not planar, as is shown by rippled region 24 in FIG. 3, some of the connectors 22 will not be electrically connected to circuitry on the substrate 14. Rippling of the substrate 14 is a significant problem in organic modules that use a polymer tape or the like as the substrate. Rippling of the substrate 14 can occur even when stiffeners 10 are affixed to the substrate if the stiffeners are not securely connected to the adhesive 12.